Posted
by
samzenpus
on Thursday April 17, 2014 @07:07PM
from the riding-the-waves dept.

First time accepted submitter Amtrak (2430376) writes "MIT has created designs for a nuclear plant that would avoid the downfall of the Fukushima Daiichi plant. The new design calls for the nuclear plant to be placed on a floating platform modeled after the platforms used for offshore oil drilling. A floating platform several miles offshore, moored in about 100 meters of water, would be unaffected by the motions of a tsunami; earthquakes would have no direct effect at all. Meanwhile, the biggest issue that faces most nuclear plants under emergency conditions — overheating and potential meltdown, as happened at Fukushima, Chernobyl, and Three Mile Island — would be virtually impossible at sea."

We could stop wasting the fuel you call waste, and using it completely instead. What we do now is like bringing in oil, burning off the diesel and ignoring the gasoline, kerosene, and all the other fuels it contains.

We already have very advanced containment systems. There's nothing about them that would be unsuitable for oceanic use, aside from requiring a whole lot of floatation. The containment system at Fukushima wasn't even close to modern, yet it did a pretty good job anyhow. Hell, the system at Three Mile Island contained nearly all the radioactive material, and that was 35 years ago.

With even the Mark 1 containment building found at Fukushima (which was 40 years old; the same age as TMI), an incident like Chernobyl (which had *no* containment building) wouldn't have been nearly as bad. Compared to modern containment buildings though, Mark 1 isn't even *last* generation; it's outright obsolete.

Meanwhile, the biggest issue that faces most nuclear plants under emergency conditions â" overheating and potential meltdown, as happened at Fukushima, Chernobyl, and Three Mile Island â" would be virtually impossible at sea."

Simply being at sea doesn't prevent the cooling problem. Remember, Fukushima was right on the ocean. The problem is that the cooling system has to have at least two loops. An internal loop of coolant (usually water, though salt has also been used) actually travels inside the reactor. Consequently it picks up some residual radioactivity from being exposed to all those neutrons flying around. You cannot just use this single loop for cooling, or else you're releasing this radioactive coolant into the environment.

A second external loop of coolant cools the internal loop via a heat exchanger. This external loop picks up nowhere near as much radioactivity, and the coolant (water) is safe to dump back into the environment.

If it were just one loop, you could come up with a clever design using thermal expansion to make the water flow through it to provide passive cooling in the event of a pump failure. But with two loops (and the inner loop being closed), you're pretty much reliant on active pumping to remove heat from the reactor core. The problem at Fukushima was that power to these pumps failed, and backup generators designed specifically to supply power in that scenario were flooded and their fuel source contaminated.

I don't see how putting the plant on a floating platform helps in this scenario, unless you're willing to open up the primary cooling loop to the environment and just dump water straight into the reactor (with the resulting steam carrying both heat and radioactivity out). Which was pretty much what they ended up doing at Fukushima. If they'd done it before the cladding on the fuel rods melted, we'd only be dealing with a small amount of radioactive water (deuterium, tritium, etc) being released into the environment as steam, instead of fission byproducts being directly released. So I don't see how being by vs on the ocean makes any difference for this scenario.

Maybe you could design the steel containment sphere to act as a heat sink, allowing sufficient cooling when submerged? But the containment's primary job is to contain what happens inside. That's why it's a sphere - it encloses the largest volume for the least amount of material and surface area, and its mechanical behavior under stress are very easy to predict. This is precisely the opposite of what you want from a heat sink. You want the most surface area for a given enclosed volume. Which makes me suspect that the steel containment could only operate as a heat sink if you're willing to compromise its protective strength somewhat.

The other problem I see is that putting it out at sea hinders accessibility. Meaning more mundane events like a fire, which are trivial to handle on land, become much more problematic at sea.

Reprocessing has not been done because Peanuthead declared it to be illegal. Meanwhile there is no rush to reprocess because new fuels is so cheap from bot mined supply and recycled from Cold War weapons through the Megatons to Megawatts program. While we wait for reprocessing to get cheaper and fuel to get more expensive, there's storage at Yucca Mountain, which is finished and waiting to be opened.